1. Field of the Invention
The present invention relates to processes for fabricating a semiconductor light-emitting device. More specifically the present invention relates to a method of fabricating GaN-based thin-film chips using laser ablation.
2. Description of Related Art
The sapphire substrate is the main substrate of growing GaN-based LED, but its electrical conductivity and heat dissipation are relatively poor. The poor electrical conductivity forces traditional LED to adopt lateral structure, which causes the current congestion, and poor heat dissipation limits the power of light-emitting device. Using laser tilt-off technique to remove the sapphire substrate to make a vertical structure LED can solve the problem of heat dissipation effectively, but the yield is usually very low. In addition, the stress is from the difference in thermal expansion coefficient of sapphire, GaN films and the support substrate, so the GaN films are easily broken when sapphire substrate is removed. Generally, finding as corresponding bonding method and a support substrate which has a matching thermal expansion and good electrical conductivity and thermal conductivity can solve the problem. But since the bonding interface is not smooth and the gap is small, there will be a pulling force to GaN films during the laser lift-off process and the damage and rupture of GaN films may occur. A traditional method is used by bonding the epitaxial layer on the sapphire with the electrically and thermally conductive substrate directly and then removing the sapphire substrate, but the yield of the chips is very low. And the method cannot solve the stress in the process of laser and leads to cracking of a large number of chips.